This proposal examines critical variables which are known to influence the development of obesity in man and other animals. We will focus on the contributions of insulin, diet composition and exercise in the development of adipose cellularity and obesity. How do these variables affect and how are they affected by food intake? These factors will be examined in genetically obese and lean rats, in genetically obese and lean rats made diabetic with alloxan and in rats that became obese by eating high fat and high sucrose diets. In addition, we will study non-shivering thermogenesis in genetically obese and lean rats lesioned in the lateral area of the hypothalamus to study the mechanism by which they lose weight and maintain a lowered body weight.